text:
How do FBOs Work?
As a student pilot, there are many things taught in training, but I've found that one of the things missing from training is "real world" flying. For example, I don't really know what you are supposed to do when you land at an airport and you are not just taxiing back for departure. Say you need to top off your fuel tanks, what do you do? When tower says "say parking", what if you don't know where you want to park? How do you know where you can park your aircraft? Can you just pull up to an FBO and expect them to show you to a parking spot, or do you have to call ahead of time or on the Unicom? How do you tell them that you want fuel? If someone could just explain basic FBO operations and how to park and fuel up etc, that would help me out a lot. Thanks!

Closely related

It depends on the FBO in question, but I'll outline the experience I've seen in the real world flying to various types of airports. Ill split it into two scenarios "big airports" and "small airports"
Big Airports: Generally at towered fields (think Class C, D and B that support GA operations) after landing (if you dont ask for a new clearance) they will say "say parking" at which point they will expect you to tell them where you are going. Like any other part of a flight this takes some pre-planning and FBO's are listed on places like airnav or in foreflight. This will allow you to pre-select an FBO based on services or fuel prices. If you land without knowing (say a diversion etc.) you can simply respond with "I need fuel" or "FBO" and they will tell you where to go.
At busy airports or airports where I suspect parking could be an issue I will typically call ahead and confirm there are spots or confirm they have the services their site says they do.
At bigger fields they often will have a marshaler to direct you on the apron you can tell them you need fuel once you shut down your aircraft. If there is no one to direct you its often fairly obvious where you should park (big open area in front of the building). Once parked if you are not greeted you can either try to hail them on UNICOM or walk inside and ask for fuel.
At bigger fields you are likely only able to get on and off the field through the FBO, they tend to be 24 hours and they will want their fees!
Small Airports: At the smaller un-towered fields (think 3000ft and under single strip out in the middle of nowhere) there will generally be only one maybe two options for parking/FBO's. There is often only one apron and it should be pretty obvious where the tie downs are. If you ask for fuel on the UNICOM after landing they will likely send the line kid in the fuel truck. Half the time they will send the line kid to point to parking but I would not expect it unless I ask over UNICOM. There is a good chance the airport is unattended and you may just need to park where you can and remember the UNICOM frequency since its likely the gate code. These fields often have self service fuel along with trucks since they may be unmanned.
I'll call small airport FBO's if I have questions about the local area, want to make sure courtesy cars are available or they actually have fuel in the storage tanks (yes sometimes they are out of fuel). However there are plenty of cases where I have just flown into a field, parked, and poked around the local area without calling or even speaking to anyone in advance.

smaller = 3000ft lol. GA is sooooo different in the US than the UK.

@Jamiec I say that as its been the general limitation (insurance imposed) from most flight schools I have rented from in the past. There are plenty of 2000-2500ft. strips around in the US but its also pretty easy to get cleared into a class C or D field in an Archer and have 7000ft. to work with.

@Dave thank you so much for your thoughtful response. Just to make sure I understand- you don't need to tell them you're coming to their fbo over the Unicom when you land? you can just pull up and they will deal with you?

@GeckoFox1001 in my experience yes, the reality is they may have a radio monitoring the tower freq so they may even know you are coming.

@Jamiec: In the western US, a lot of fields are at what would be considered high elevation in the UK (heck, many are higher than the peak of Ben Nevis), so you often need the extra runway.

If there is more than one FBO, ATC isn't allowed to suggest one or the other. If you just say "The FBO" or "I want fuel" you'll get a list of options and you have to choose one to be directed towards. Of course if there's only one FBO on the field we're allowed to send you to it.

Also worth noting that if you don't need services, look out for transient parking in your flight planning. The larger fields won't have any because of agreements with the FBOs, but some smaller municipal fields will just have places to park. They're usually marked in a different color or with text on the pavement to contrast from normal, tie-down rented parking spaces. Fees vary; many times it's on the honor system to deposit an envelope with cash in a box.


text:
Why did Airbus mix "colored light means ON" and "colored light means OFF" in the overhead panel?
Disclaimer: I don't have a real Airbus A330 at hand, nor am I a pilot.
After having crashed twice due to icing in rainy weather (not to talk about that here) with an Airbus A330 in X-Plane 12 simulator, I realized that I did not turn on anti-ice protection!
While I still trying to find a good manual, I had tried to get accustomed with the panel and its logic, realizing that when some light are off, it actually means that the underlying system is on, so at some point I had made the erroneous decision that "all lights off" is a good state for the panel.

Still it seems that it's easier to spot a single light that is on, rather than finding a single light that is off.
The situation may be more interesting if the light, but not the underlying system fails.

So I wonder: Why did Airbus mix different logic models in one panel?

If you cannot find a good manual for flying the A330 in flight simulators, try looking for an A320 manual instead. There are far more A320 simulations out there and the two types are very, very similar in most aspects.

The logic for illumination of buttons on the overhead panel is called the dark cockpit concept, previously also called the Forward-Facing Crew Cockpit.
It was originally developed by Airbus for the A310, which eliminated the flight engineer position of the early A300 variants and therefore had to simplify system operation for the two pilots using a simple overhead design combined with electronic monitoring and warning instruments:

Airbus improved the cockpit layout, allowing a two-pilot flight crew to operate the aircraft without the need for a flight engineer. The new concept, called the Forward-Facing Crew Cockpit [...]
This A310 “glass cockpit” used six computer-driven cathode ray tube displays to provide the captain and co-pilot with centralised flight and navigation information as well as monitoring and warning data.

(Airbus Technology Leaders (1977-1979), web.archive.org)
The general principle for the overhead panel is that when all lights are extinguished, the systems are in their normal state for flight. If you see lights, they are colour-coded to indicate any of the following:

Dark Cockpit Concept
No White Lights
System is set
Fit to fly
The state of the Lights and information provided on display units are color coded to indicate the status of the system, or the nature of the information

(ICAO/Airbus FOSAS presentation)
As the anti-ice is only selected temporarily1, it will be illuminated in blue while ON. This serves as a reminder for the crew to select it back OFF when it is no longer needed.
Note that the indications on the overhead panel are only there to catch your eye, not to give a full overview of the current system state. This is done using the ECAM:

The Electronic Centralized Aircraft Monitoring (ECAM) system is a main component of
Airbus’ two-crewmember cockpit, which also takes the ”dark cockpit” and ”forward-facing crew” philosophies into account.
The purpose of the ECAM is to:

Display aircraft system information
Monitor aircraft systems
Indicate required flight crew actions, in most normal, abnormal and emergency
situations.

(Airbus A320 FCTM - Operational Philosophy - ECAM)
Today, all Airbus aircraft share this concept for reasons of commonality, which allows pilots to transition between different models very easily:

Another standard Airbus feature is the ‘dark cockpit’ concept whereby lights only show on the overhead systems management panel to indicate where an action is required. Overall the A330neo and A350 cockpits share a similar layout.

(Airbus: A330neo cockpit - Commonality with A350 innovations)
Some other aircraft manufacturers also followed this principle, e.g. ATR (which shares a lot of avionics with Airbus), McDonnell Douglas (starting with the MD-11) and Bombardier:

Dark cockpit
The Bombardier Vision flight deck leverages a dark cockpit philosophy. Featuring push-button annunciators that remain dark in normal operation, toggle switches positioned forward for flight and knobs that are in the 12 o'clock position when in AUTO, pilots can have situational awareness at a glance and focus on flying.

(The Bombardier Vision flight deck)
Boeing still follows are more traditional design, where pushbuttons always indicate their state, even when in their normal setting, e.g. here is the window heat section of the Boeing 787:

(cropped from source)

1 Engine anti-ice should be selected ON whenever the aircraft is in icing conditions: TAT < 10°C and visible precipitation / clouds. Wing anti-ice should be selected ON when airframe icing is visible (e.g. on the black stick between the two forward cockpit windows).

A great answer; I just doubt that AIrbus still uses CRT (Cathode ray tubes) (e.g. for weight and size reasons). --  A question that remains is whether the pilot sees the buttons as shown (e.g.) in  https://i.sstatic.net/e5anw.png, or is it just for illustration showing the possible illuminations? In the view I had (in the simulator), it  was not obvious whether lit would mean "ON" or "OFF".

@U.Windl CRTs were replaced on older aircraft (source). You can see the not illuminated text on the real buttons, see e.g. this image where you can recognize the "OFF" on the buttons (source).

I think this gets into Human Factors and other usability issues, but as an interface designer as part of my job I can say how I would approach this... I don't have (and I don't think it is published) specific information on Airbus engineers thought process...
The lights indicate a "not normal" state. In the case of anti-ice, the "normal" state is anti-ice is off, so the light indicates when the anti-ice is on.
For your second picture, the Engine Bleed normal state is "ON", and "OFF" is indicated as something abnormal. Same with the pack fault, the "fault" indication is abnormal and therefore lighted.

Agreed, No specific knowledge on Airbus, but when we were working on upgraded onboard displays for the space shuttle back in the day, the rule was "quiet dark" - as you say, light on if attention is needed.

Well, during winter "anti-ice" may be "normal". As I said: I wasn't expecting icing when it was "just raining" (BTW: Chicago on Jan 1st, near 0:00 UTC)

I think you misunderstand what "anti-ice" means or how airframe icing works... I've gotten airframe icing on a warm day (at ground level, at altitude it was much colder).

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

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What jet is pictured on the FAA pilot certificate?
The front of the FAA pilot certificate shows two aircraft.  One is the Wright Flyer.  The other appears to be a 2 or 3 engine commercial jet.  What model of aircraft is that jet?  The engines look longer than any of those in common use today.

https://books.google.cz/books?id=UOhMBNM5LI8C&lpg=PA31&ots=WegaBa5_GK&dq=%22airmen%20certificate%22%20%22wright%20brothers%22&pg=PA33#v=onepage&q&f=false "a jumbo jet"

@757toga - I posted it without comment because I don't know anything about planes

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Why was the minimum turbulence intensity that commercial airliners have to withstand increased?
From 50 fps turbulence intensity at VC to 90-100 fps turbulence intensity at VC. The amended FAR design criteria was introduced in 1980 or 1981 for commercial airliners. What prompted this change?

Assuming you're referring to FAR 25.341?

I believe so. I've seen the 90 fps design criteria be referenced in documents from 1980 or 1981 at the earliest. I'll try see if I can dig those up later.

The FAA made that change in 2015.
Link to historical revisions of FAA regulations, specifically 25.341 gust and turbulance loads. You can see the 90fps was not in the 1996 revision, 1984 revision, or original 1965 rule.
Link to Amendment Number: 25-141, Effective Date: 02/09/2015 https://drs.faa.gov/browse/excelExternalWindow/C86DBFEBB41D816F86257DE80072BA20.0001
If the above link breaks try https://drs.faa.gov/browse/FAR/doctypeDetails browse to 25.341 Amendments - 25-141 (02/09/2015) , 25-86 (03/11/1996) , 25-72 (08/20/1990) , Initial (02/01/1965)
Rule making explanation. Generally just aligning FAA and EASA requirments with little to no practical effect on current production aircraft.
https://www.federalregister.gov/documents/2014/12/11/2014-28938/harmonization-of-airworthiness-standards-gust-and-maneuver-load-requirements

According to the FAA, "The final PSD continuous turbulence criteria were based on those studies and were codified in Appendix G to part 25 in 1980."
This matches the timeline you suggest, but the Appendix released in 1980 does not specifically mention 90fps.  (See Amdt. 25–54, 45 FR 60173, Sept. 11, 1980.)
Bottom line: research through time over the actual nature of turbulence and analytical procedures for modeling it resulted in the rule change, as explained in sufficient detail the first reference.


text:
Were the Airbus A320 rudder hardover issues fixed after Indonesia AirAsia Flight 8501 crashed due to uncommanded rudder deflection?
Indonesia AirAsia Flight 8501 crashed when the rudder made an uncommanded deflection 2 degrees to the left:

When the crew was required to fly the Airbus A320 manually, there was
an unexplained nine-second delay between the start of the roll and
either pilot attempting to take control. After nine seconds, the
aircraft was banking at a 54° angle: the rudder had deflected 2
degrees to the left, causing the aircraft to roll.

(Wikipedia)
I see very little discussion about the uncommanded rudder deflection, instead people were quick to blame the pilots. Was this rudder hardover issue fixed?

This was not a rudder hardover  event. Have you read the full NTSC Reoprt? http://www.aaiu.ie/sites/default/files/FRA/KNKT%20Indonesia%20Final%20Report%20PK-AXC%20Airbus%20A320-216%20Air%20Asia%20PT%20Indonesia%202015-12-01.pdf

Summary: The rudder movement (not really a hardover, since it only moved 2°) was caused by a non-approved inflight restart of the FACs (Flight Augmentation Computers) using the circuit breakers instead of the overhead pushbuttons in an attempt to fix an issue with the Rudder Travel Limiter Units. Since these actions are not approved, there was nothing to fix, and to my knowledge nothing was changed about the A320 afterwards.
Details: If you look through the final accident report, you will find a detailed description of what happened to the aircraft systems. At first, the pilots successfully fixed a "AUTO FLT RUD TRV LIM SYS" ECAM message by restarting the FACs using the overhead pushbuttons:

Between 2301 UTC to 2313 UTC the FDR and CVR recordings indicated three
Rudder Travel Limiter Unit failures occurred and triggered the chime and master
caution, followed by PIC actions to ECAM actions to reset FAC 1 and 2 pushbuttons on the overhead panel to OFF then to ON. Thereafter both of Rudder Travel
Limiter Units returned to function normally.

When the ECAM message re-appeared again, the pilots pulled the circuit breakers for the FACs (which de-energizes the FACs) and then later reset them:

At 2316:29 UTC, the FDR recorded parameters which indicate that FAC 1 was deenergized leading to the ECAM FAC 1 FAULT message associated with the 5th
master caution. 17 seconds later the FDR recorded parameters indicate that FAC 2
was also de-energized leading to the FAC 1+2 FAULT message associated with the
6
th master caution. The FAC 1+2 FAULT was followed by rudder deflected 2° to the
left, the aircraft flight control status reverted from Normal Law to Alternate Law and
the Auto Pilot (A/P) and the Auto thrust (A/THR) disengaged. As consequence, the
pilot should fly the aircraft manually.

However, resetting the circuit breakers does not activate the FAC again, unlike using the overhead pushbutton:

At 2316:39 UTC, the FDR recorded that the FAC 1 was re-energized indicated by
stopping of parameter alternation. However because the FAC1 pushbutton on
overhead panel was not reset by put to OFF then ON, the FAC1 functions remained
unavailable and all equipment controlled by FAC 1 did not operating.

Airbus explained why pulling the circuit breakers (in the wrong order) can lead to a movement of the rudder:

When the 26VAC CBs of both FAC were pulled, the loss of the 26VAC was
detected by the FAC monitoring. However the FAC logic associated to the
computation time and rudder movement inertia created a rudder movement of about
2°.
As both FAC were unavailable this rudder movement was not automatically
compensated.
If the 28VDC C/B is pulled before the 26VAC C/B, the FAC is immediately
powered off and no rudder movement can be ordered.
The rudder movement can only occur if the 26VAC C/B is pulled before the 28VDC
C/B. The ECAM message “AUTO FLT FAC1+2 FAULT” is generated with the
associated ECAM procedure asking to reset the FAC through the P/B on overhead
panel.
After the FAC2 26VAC and 28VDC CBs have been pushed, there is no more rudder
trim function available as no FAC was reset through the P/B on overhead panel. The
message “AUTO FLT FAC1+2 FAULT” was still displayed.

Roll was only an effect of a fully developed stall. The rudder did not go hardover. Air Asia 8501 did not crash due to uncommanded rudder deflection.

I see very little discussion about the uncommanded rudder deflection.

That's because it was not the issue and the rudder worked in alternate law, the problem was: recovering from a fully developed stall. From this answer:

The Air Asia captain did realise they were in a fully developed stall, and immediately pitched the stick forward. He was an ex military pilot. The issue there was:

Language. An Indonesian national using English to instruct the French co-pilot to Push Back.
No direct force cue that the copilot was pitching back while the captain was correctly pitching forward. Airbus averages out conflicting stick inputs if no pilot has taken exclusive control by pressing the override button > 20 seconds.

A cracked solder joint in one of the printed circuit board had caused a repeated malfunction in the rudder system, which the pilots attemted to cure by pulling circuit breakers, causing the autopilot to disengage.

The AirAsia crash was not a flight control or an aircraft design issue.
The crew disabled multiple flight control computers in flight trying to resolve a minor (but persistent) computer issue the aircraft had. As a result of computers being shutdown simultaneously, the aircraft reverted into what is called an Alternate Law which caused autopilot to disconnect and aircraft to deviate from intended flight path. For some reason nobody was monitoring the flight instruments (ie. looking forward) while the computer reset was being attempted. The reason might be that the circuit breaker panel is located behind copilot's seat. At the time the captain had left his seat to perform the reset and the copilot was supposed to be flying the aircraft.
"Pilot error" is a quick blame for pilots who were startled with unforeseen situation. As usual, you can go deeper and ask why licensed pilots made the said mistakes. The fundamentals of the crash are not unlike that of the famous Eastern Air Lines crash. In both cases a very survivable technical issue led to an accident because of poor CRM, which can be attributed to insufficient training and procedures, as identified in the final report.


text:
I heard that the Yaw Damper is critical to flight safety. Why then are most planes allowed to fly with one (out of two) dampers inoperative?
For example, a twin engine plane  would not be allowed to fly if one engine was inoperative, in case the only working engine failed mid-flight.
Why then are planes such as the 737, 747, 757, and 767 allowed to fly if one yaw damper is inoperative?

Yaw Dampers are designed to counteract Dutch Roll.  Dutch Roll is a continuous yawing and rolling movement that can be experienced in swept wing aircraft in varying degrees of severity.
Dutch Roll can be Stable, Neutral or Unstable.  Only aircraft with unstable Dutch roll characteristics have the need for robust redundancy in their yaw damper systems as total failure could lead to loss of control in certain speed ranges.
Aircraft that have Stable or Neutral Dutch Roll characteristics can dispatch with only one yaw damper because if it failed the subsequent Dutch roll would not be a flight safety hazard.


text:
What is "company compensation fuel" and "pad fuel"?
I tried to find the definition of these fuels but I could't.
Does anyone know about company compensation fuel or pad fuel?
In which document can I find the definition of these fuels?

What company are you asking about?  Do you work for this company?

Those are probably not common terms and probably relate to only a few companies.

Thank you, Mike.

You really need to add more context, otherwise your question might be closed as "unclear"

Company Compensation Fuel
This is a term, which seems to be used by Korean Air. They define it on their website:

▶ Company Compensation Fuel
fuel to minimize abnormal flight occurred. Based on this, fuel consumption performance is modeled for a certain period of time, and based on this, the amount of fuel repeatedly consumed excessively compared to the flight plan is added.

(koreanair.com, translated by Google)
So this is fuel added based on the airline's experience (hence company) for typical fuel use on a given route.
Pad Fuel
I have never heard this term and Google also does not find anything related to aviation. Is it possible this was a translation? If so, could you add the original term and where you heard about it?

"pad fuel" may refer to the fuel added by the PIC above what company dispatch has mandated.  The PIC may decide the weather, traffic, etc. may prolong the flight time above what is planned.  Thus avoiding draining the mandated reserve fuel.

I suspect the "pad fuel" might refer to conditions where deicing is needed. Time spent on deice pad with engines running leads more fuel consuption than a normal taxi to holding point would.
Since this is an easily indentifiable situation with predictable effect on fuel consumption, it might be that this would be referred to as "Pad fuel".
But: as google comes up with absolutely nothing, I highly doubt my own answer.

Good theory, I didn't think about the term deicing pads!

PAD fuel is company specific and typically applies to an abnormal event taking place at or near a predefined point; e.g., ETP during ETOPS.
For example: If a depressurization event were to occur and a subsequent decent commenced, PAD fuel would be that in excess of minimum GO/RETURN fuel to reach facilities named on either side of an ETP under reduced efficiency.
It’s just another dispatch contingency similar to the aforementioned compensation fuel and is used in the same colloquial context as if supplementing or “padding” one’s bank account.

Hmm... I think reserves for events you describe are already included in the "usual" reserves. I know my own answer is speculative, but can you give any source for your claim?

No. The “usual reserve” you state is regulatory. ETP padding is both discretionary and variable, thus calculated outside of reserve minimums.
The definition I provide is per company FOM and may not be shared via open forum. Proprietary rules prevail. Notwithstanding I notice a lot of guesswork here, which has no place in aviation or any academic pursuit. The aforementioned is the answer to the question – take it or leave it.

While I have no specific knowledge of these terms being used together, my first thought was that "Pad Fuel" would be fuel gotten from the local pad, and "Company Compensation Fuel" would be fuel that you purchase while away and get reimbursed for, or compensated.


text:
Why was there no thrust from the engines in the TACA Flight 110 incident?
I have just watched Mayday episode 11, season 11, "Nowhere to Land" about TACA Flight 110 incident. Most key issues of the incident are clearly explained in the episode:

Why both engines turned itself off,
Why there was an overheating alert after restarting the engines (and they had to be shut off).

But, there was a short period of time between restarting the engines and manually shutting them off when pilots were claiming that (based on instruments) both engines are working (spinning), but there is no power / thrust being generated by them (i.e. plane has no power).
Either I missed something or this small issue was not explained.
What does it mean that engines are working (spinning?), but not generating any power? Does this refer to situations where only compressor fans are spinning in the cold section, but there is no fuel burnout in engine's hot section? Or is it something else?
And what can cause such situation? If I am not mistaken or not missing anything -- episode explains issues with heavy rain and hail that damaged fans, but says nothing about fuel distribution system, engine ignition or any other issue that could cause spinning engine to not generate any thrust.

To generate thrust, engines need fuel and air: a spark will ignite fuel (by getting heat, above the ignition point), which burn with the oxygen in the air.
On this (and other incidents), together with air, also rain (and hail or snow) in the engine, so the spark is not enough to ignite the fuel, and so the engines stop working. So, this is the important factor: air and rain enter in the combustion chamber. It is not a problem of fuel distribution, it is just a problem of not being able to ignite fuel. [On car you have air filters, and air compressors, but also a very different cycle compared to jet engines]
The continuous restart means that the engines will continuously add some sparks, so that if ignition fail one, at next turn the the ignition should start again.
The spinning means literary: the engines were spinning, but this doesn't mean they can get enough energy. The article in Wikipedia tell us that they never reached IDLE power. I think the problem is that rain has blocked many of the sparks in the engines, so the engines ignited only some time, enough to get the engine spinning, but not enough to get power.

The engines never stopped spinning. As long as there is no severe damage, the turbine blades will continue to "windmill" due to the forward airflow even without ignition or combustion.


text:
Is the cockpit depicted in this movie from an Airbus A330?
I am watching this YouTube movie:

And I wonder, if it is possible to tell the aircraft being flown here, just from looking at the cockpit instruments (quite low quality) or other information that can be found in this movie?
Searching the Internet for part of the title (Miami Approach - TCAS Alert Licence to Fly) has brought me to this book at Amazon.com:

Based on the above, can we confirm that the depicted aircraft is in fact an Airbus A330?

I'm not sure I would agree with calling it a movie, nor the last link a book.

@CGCampbell Hm... "clip" and "printed guide"?

@trejder The Amazon link for is a Blu-Ray disc containing the whole documentary film from which the YouTube clip was taken.

Yes, that is an Airbus A330.
Consider the following scene from the video (0:13):

The area circled in red is the landing gear indicator and the area in green is the alternate landing gear extension. This layout and design is very characteristic for the A330 (and similar to the A340, but with a center body gear, see e.g. this image; you can also clearly see only two thrust levers, further excluding the A340). For reference, compare to this picture of an A330 cockpit from Wikipedia:

(cropped from Wikipedia A330 Cockpit)
Note: this picture shows an older aircraft with analog standby instruments (to the left of the two central screens). The aircraft in the video already has the modern digital standby instrument.
For more details on how to distinguish different Airbus cockpits, see What aircraft has this cockpit?

Yes. Combined with the wing views and the callsign (LX64) it is clear that this is a Swiss A330.


text:
What steps are needed to communicate with ATC on an A320?
In the description to this video, Captain Joe says that it took this inexperienced person 20 minutes to establish radio contact with ATC (in an A320 simulator).
This seems like an awful lot of time just to find and push the "push-to-talk" button. So, is there something more to it, like having to enter the right frequencies or something?
In the hypothetical case described in the video (passenger having to fly the plane), would it be enough to push the PTT button to establish contact with ATC, or are there other steps that need to be taken?

On Helios Flight 522, Andreas Prodromou had fifteen minutes to figure out how to work the radio but didn't manage it before the crash.  And he had a CPL!  https://en.wikipedia.org/wiki/Helios_Airways_Flight_522

You need to even realize that you have to push a button to talk. Not everyone grew up with ham radio, CB radio, or walkie-talkies, especially nowadays where everybody has a mobile phone.
You need to find the PTT button.
You need to select where you want your headset to be routed: you can talk to your co-pilot, you can talk to ground crew, you can talk to the cabin crew, or you can talk to you radios.
Note the plural above: the plane has multiple radios. You need to select the right one.
You need to know the frequency of the ATC entity you want to talk to.
You need to tune the radio (the right radio) to that frequency.
Every radio has an active frequency and a standby frequency. You need to make sure that you change the right one. (Either change the active one, or if you change the standby one, you need to make that one active.)
You need to realize that radio is a shared medium, and that only one person can talk at any one time, and that you need to wait for a break.
Depending on how busy the frequency is, you might not even recognize where the pauses are, or you might not be able to squeeze yourself in because you are not used to talking that fast and efficient.

I consider myself technically adept, and I used to do a little bit of CB radioing in my youth, but I'm not sure if I could figure all that out in 20 minutes.

And that's just one of the reasons why a pilot has to be certified for a specific airplane to be able to fly it effectively. They're all just a bit different and once you're on your way you don't necessarily have the time to figure out what buttons you need.

Surely any radio frequency would do as long as you say "Mayday Mayday Mayday"? Anyone hearing you would respond on the same frequency right? And then guide you what to do next?

@DavidPostill: If no one is listening at all (for example because you've fumbled the radio channel to some unused frequency), then no one will respond.

@Kevin That's why I said "anyone hearing you". The point being that the channel doesn't matter for Mayday as long as someone can hear you. There is no wrong channel for Mayday, right?

@DavidPostill A channel no one's on is definitely the wrong channel for a Mayday.

@DavidPostill a channel where nobody can hear you?


text:
What is the recommended procedure to land a taildragger in a crosswind?
Almost 20 years ago I helped a friend (who recently passed away from an unfortunate home accident) ferry a 1948 Stinson from Córdoba, Argentina, to Buenos Aires. We had to make several stops to refuel (while classifying them by how many dogs and cats came out to greet us), and at one of the fields the crosswind component was rather strong. I can handle just about anything thrown at me when flying a tricycle gear aircraft, and went through taildragger endorsement training in a Citabria, but it was a challenge to get this bird safely on the ground.
Thinking about that today, I thought it would be good to gather guidance from experienced taildragger drivers on what is the recommended procedure to safely land a taildragger in a crosswind.

Approach and touchdown should be similar.  On the roll-out once rudder authority is less than side force a little more brake on the lee side might help.  But it might be good to have a little patch of clear area on the windward side in case it gets turned.

While there's general advice out there some of it varies from aircraft to aircraft depending on capabilities, so this is perhaps too broad.

Oh I got turned alright, but it was at the final destination. It was dark, the chart said they had runway lights, but said squat about not having enough money to buy bulbs. I darn near landed on a road next to the field. Good thing the little store at the end was open and lighted. Nothing either about a dirt runway turned to mud. 450 degree groundloop, no damage. "Another happy landing in South America!" :)

@GdD That's true, but nothing wrong with getting opinions for various aircraft, with notes on their quirks. :)

Well..... questions asking for opinions are actually off-topic @JuanJimenez. You might get better results in a forum.

So put it up for a vote.

I think it's a good question.

That Stinson does have a huge fin doesn't it --

Not just that, it was on the X registry, experimental, and had been rebuilt by an amateur mechanic. That i only found out when i arrived at the field to install a radio i brought from the US. I had my doubts, but i figured Argentina is like Texas, one big grass runway, just avoid the cow chips... It was an interesting adventure. Lost 1 qt of oil per leg, and it was "IFR" all the way

Huge fin and large slab side aft CG.  Definite side force imbalance issues here.  Pilot should not feel bad.  Rudder looks a little small too, may be a "slip turner" philosophy going on here.

"know your limits" and have no fear of aborting to pick another option.

My favoured technique in strong crosswinds, perfected in many hours of glider towing in Super Cubs, Citabrias and Pawnees, is to wheel it on tail high, wing down, and balance it like that until the speed drops enough to lower the tail, then put the tail down and plant it firmly with aft stick.
In those conditions it's desirable not to have the wing at high AOA when ground contact and especially tailwheel contact (traction) is marginal, as you get when you do a 3 point landing.  By wheeling it on (wing down obviously), you get firm mainwheel contact right away, AOA is low so gusts won't pop you back into the air, and you still have air rudder authority.  The technique keeps the transition from air rudder authority to tailwheel ground traction as short as possible.
Wheel landings seem difficult but are actually easier than 3 point once you learn the trick (For the trick to be revealed, send 10$ to my Paypal @...).  Actually, the trick is simply that you PUSH when the main wheels are a foot or two in the air. You'll go plop and won't bounce or skip.  In a crosswind, it's a little trickier because you have to push while holding a sideslip and you find yourself balanced on the one into-wind tire, with your feet and hands going a mile a minute.  As you slow down the other main wheel will come down, then as soon as you slow enough to be able to plant the tailwheel without becoming airborne again, you plant the tail and full aft stick.
Also, be ready to use brake during the rollout in case rudder and tailwheel authority are both insufficient to stop a swing (this can happen on wet grass for example).
Takes some practice, but once you perfect this technique you will have much more confidence in strong X winds.

It's that "takes some practice" that gets me worried. 'Course, it calls for dual with a good instructor. :)

Best way is to find a glider club and join up to tow.  Best skill honing activity you can possibly do for both landings and low speed handling in the air.

Oh, I feel another question coming... :)

I've seen impassioned arguments for both wheel landings and 3-point landings for taildraggers in crosswinds, depending to some extent on the specific type of aircraft involved.  Most arguments favor a wheel landing, but others point out that you will have a vulnerable moment as you are decelerating and the tail is starting to lower to the ground, where your rudder authority will be poor, so it's better to keep just the aircraft in the air till it's ready to land in a 3-point attitude, and then "plant" the tail as firmly as you can.
One thing is sure, you don't want to allow ANY sideways drift at the moment of touchdown.  At the moment of touchdown, the nose MUST be aligned with the direction of the runway and the aircraft MUST not be drifting sideways toward either edge of the runway.  In light-to-moderate crosswinds this is best accomplished with a wing-down cross-controlled slip.  In strong crosswinds a combination of wing-down slip plus some crab, with the crab "kicked out" just before touchdown, may be feasible and may be the most effective technique in some tailwheel aircraft according to some authors (source, Plourde, "The Compleat Taildragger Pilot".)

I'm pretty sure I've heard the case for 3-point landings in x-winds being made by at least one Stearman (PT-17) pilot in particular

I don't agree with the poling forward recommended by John K above "...PUSH when the main wheels are a foot or two in the air."
One day when the lighting conditions are different or you just misjudge the height (and who has not done that) you will come a cropper. Maybe a few inches if you are a good stick and current with your 'eye in'.
As for wheel landings vs three pointers in strong crosswinds, I would go with wheelers every time unless precluded for some type specific reason. My father told me you did not wheel the Auster but he did not elaborate as to why.
Having said that, I have 100 hours or so in the Pitts S1 and have never wheeled it. My S2 instructor (the S1 is single seat) advised me that "until you have 300 hours in it, if it looks windy enough that you might have to wheel it on, just don't fly it".
He did demo one in the S2. We were going awfully fast.
This is what I recommend for the C185 which is the tailwheel type that I have the most time on.
The secrets are - Weight on both main wheels, ailerons into the wind and keeping it dead straight! The last two apply to takeoff as much as landing.
In a fully loaded C185 you need 75 kts for a good wheeler. You want to touch down tail high.
Fly it in with confidence, wings level and crabbing down the extended centreline. I forget if I used full flaps or 3/4. It was a long time  ago.
With only just enough flare to avoid hitting hard, close the throttle, de-crab and lower the upwind wing enough to stop any drift all in one motion. Do not 'hold-off" - avoid any float.
The aircraft will touch down on the upwind wheel. Immediately 'press' the aeroplane firmly onto the ground, BOTH wheels. You cannot do this too quickly.
AFTER both wheels are firmly on the ground apply aileron into the wind, all of it in a 15-20 kt crosswind and keep it there.
Apply rudder and if necessary differential braking to keep dead straight. This is done by 'eye-foot' coordination as required but will usually be anti-weathercocking rudder and brake. eg With a left crosswind the aeroplane will want to turn (yaw) left into the wind. You may need all the right rudder and then some right brake as well to stop it. Show the aeroplane that YOU are the boss. Leave the into wind aileron in place.
At all costs avoid rolling along on one main wheel because the 185 will often run out of rudder and the brake you will then urgently need will not work because the wheel will be off the ground!
Let the tail come down with about neutral elevator. Certainly don’t push down elevator to delay this - forward stick will unlock the tailwheel in some types eg T6, Mustang and Winjeel.
After the tailwheel is on the ground apply back stick and continue to keep it dead straight. If the brakes are weak or nonexistent (like a stock Tiger Moth) you may need full rudder and blasts of power to prevent weathercocking.
The above technique, with variation will work for most tailwheel types.  However none of the other types I have flown need as firm a 'press' onto the ground as a heavy C185; eg the T6, the Chipmunk, the Winjeel (look it up), the Tiger Moth and the C188 only need a 'check' forward after touchdown. Also some have more powerful ailerons than the 185 and you do not want to lift the downwind wheel off the ground. (or roll a Pitts into a ball!)
However it is vital that you use enough into wind aileron so that you never, ever, ever let the into wind wing lift.
In an aeroplane with powerful ailerons, be careful not to use too much if you use any on the takeoff roll and be ready to centralise instantly as you get airborne.


text:
How could the Helios 522 passengers have survived so long without oxygen?
I've noticed some strange inconsistencies regarding the documentation of Helios Airways Flight 522.
So first:

Autopsies on the crash victims showed that all were alive at the time of impact

But then:

The emergency oxygen supply in the passenger cabin of this model of Boeing 737 is provided by chemical generators that provide enough oxygen, through breathing masks, to sustain consciousness for about 12 minutes

So, the oxygen masks in the passenger cabin automatically deployed at 18,000 feet, probably around 09:20. The aircraft did not impact until 12:04. 2 hours, 44 minutes later. Obviously the oxygen masks didn't keep them alive for that long, so:
How could they have survived so long?

I think you are confusing "alive" with "conscious".

@GiacomoCatenazzi Not at all. If there is no oxygen to breath for almost 3 hours, you will not be alive.

"If there is no oxygen": There is oxygen, the same percentage as at sea level, but at lower pressure. This allows to use air from the outside to breath in the cabin, after compressing it.

@Snowman I think you are looking at climbing data. These levels are assuming acclimatisation,

Hence the advice drummed into pilots during training: get your mask on first, deal with everything else afterwards. At an airline I worked for, every single flight saw the pilots test the mask oxygen flow, and practice putting the mask on quickly. Not sure if this is universally done though.

Consciousness requires quite a bit more oxygen than merely being alive.
Human beings can last remarkably long with very little oxygen, but not remain conscious. And lack of oxygen will soon enough cause permanent damage.
The passengers may have been alive, even if they were not conscious, but they could have been anything from temporarily incapacitated to on the way to certain death by the oxygen starvation, even if they somehow had been rescued before the crash.

A body can go ~5 minutes without air before irreversible brain damage occurs. But a damaged brain can still keep the body "alive" - at least alive enough for the autopsy to detect them as such at the time of the crash. And that is total oxygen denial. In high altitude, some oxygen is still present. Not a vacuum.

To add to Daniele's answer, from the final report:

The  forensic  report  concluded  that  the  aircraft  occupants  had  heart  function  during  the  impact.    The  report  noted  that  this
    did  not  necessarily  imply  that  they  were alert.    The  report  further  estimated  that  they  were  in  deep  non-reversible  coma  due  to
  their prolonged exposure (over 2.5 h) to the high hypoxic environment.

So, again, saying that they were alive does not mean that they were well.

That must've been quite the morbid scene, an entire airliner seated full of comatose or brain-dead, but still alive, individuals.

@NilsGuillermin If it's any consolation at least it means they didn't suffer.

I wonder how exactly one can determine if someone's was alive at the time of impact?

Physiological reactions prior to death leave different results from postmortem trauma. @ebrohman

It's science of autopsy.  You can tell whether someone was dead then was frozen, or someone was frozen, then died because of the cold.  Injuries affect a dead person differently than a live person.

Tissue pathology in a post-mortem clearly shows whether cells were 'alive' or 'dead' from O2 deprivation at time of death.

Here is a list of those people who survived as stowaway in the unpressurized and extremely cold wheel well.
On June 19, 2015 an unidentified male who was 24 years old survived 11(!!) hours in the wheel weel of British Airways Flight 54 from Johannesburg to London. As you also see, this is incredible because as you suggested most of the people simply die.
Another surviving victim without permanent damage was paraglider Ewa Wiśnierska, who survived half an hour long in a thunderstorm cloud at a height of nearly 10 000 m (33 000 feet).
You must also be aware that the passengers breathed pure oxygen allowing the oxygen supply to enter the blood and increase the level in the organs before they passed out, so the permanent effects of hypoxia may be delayed.

The cold actually lower the oxygen consumptions. Childs have been known to remain UNDER water at frigid temperatures for long periods of time before being revived without any permanent damage.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How does a Boeing 737 look like at night from 2000 meters away?
I am asking about the current crash of a Boeing 737-800. Due to the unfortunate crash of Ukrainian 752, I am trying to figure out what can be seen from the launch pad when they decided to shoot the plane. I determined the plane was at 4620 ft AGL and climbing. According to my calculations, the line of sight distance from the operator to the plane was 2058 meters = 6729 ft away.
So I want to know how a 737-800 looks like from the ground 6729 ft away at night.
I would like to know if it is possible to mistake a 737-800 for anything else from that distance at the night time with full visibility. Can anyone provide a picture of that?

The real question is: Are such anti aircraft missiles really launched using a visual target? I was under the impression that they generally use radar and heat signatures.

It doesn't matter what it "looked like", it was something flying towards an area of interest, the military took (incorrect) action and it resulted in the deaths of 130+ civilians. At +1 mile at night it wouldn't look like anything other than some loud blinking lights.

For something shoulder-launched, the operator might acquire the target visually, but the missile guides on IR. Big SAM's typically acquire & guide on radar.

A mile away at night?  Basically you are just going to see the lights.   Is there any claim that anyone was actually trying to look at the plane visually?  What was the moon's phase, elevation, and azimuth relative to the plane as seen from the spotter's position?  Was the sky clear of clouds allowing uninterupted moonlight?  If so the plane itself might have been fairly visible-- if anyone was looking.  Perhaps much more relevant-- would an attacking enemy warplane have any lights on?

@Michael The largest visually-guided SAM that comes to my mind is the 2K22 Tunguska, and even then it is more of a backup mode.

"I would like to know if it is possible to mistake a 737-800 for anything else from that distance at the night time with full visibility" Well, obviously, it is.

The SAM site operator would've been looking at their computer screens, not outside.

@quietflyer if my experience in Israel is anything to go by, no, war planes do not have navigation/anti-collision lights on when flying into combat. They do, however, turn them on once back into friendly airspace on the way home.

At night, at that range, it will look about like a dot of light, probably with a red flashing beacon and white flashing strobe lights.
That's what you'll see from essentially every aircraft at that range at night, unless the pilot chooses to turn off some or all lights.
But you're seeing the LIGHTS, not the AIRCRAFT, at that distance, and the ability to visually identify what aircraft it is, is essentially nil.

I'm not a gunnery specialist but I would at least use binoculars before shooting at something that far away, wouldn't I?

@PerlDuck I doubt the military would rely on visual observations alone when identifying potential targets. They have radar.

The binoculars would show you a bigger dot of light with brighter flashes from the beacon & strobes. At night, the ability to visually identify an aircraft at two miles is pretty much zero unless you have some immense magnification & image stabilization.  Plus, procedurally, you'd rely on identification methods that aren't dependent on clear skies between you + the target. Thus, radar, transponder codes, airways, departure/arrival routing, voice contact, etc.


text:
How many stripes does a student pilot have?
When a student is finishing a Bachelor in Sc. Aviation, how many stripes does a student have? Can a student have stripes during his bachelor graduation or do they have to go through other PPL courses?

In the US and most of Europe I have only ever seen 3 uniform stripes for a First Officer, and 4 for a Captain.  If you are part of a school that issues stripes to student pilots it would be better to inquire directly with the school.

There is a major 141 school I know of that uses one and two bars.  I haven't a clue what they mean.

Stripes don't have any standardized meaning in between companies. If a company wanted, it could give one stripe to its most senior captains and four stripes to the office dog.
If your employer or your school has issued you a uniform, then the number of stripes that you have is the number of stripes that they decided to put on that uniform. If you haven't been issued a uniform, then you don't have any stripes.

You just gotta love Paul :) As a side note, whatever it is that you are doing, if the number of stripes matter, you're in the wrong business. Unless the business is making stripes.

I want a picture of that office dog with stripes!

Outside the military, stripes mean nothing. They are not earned rank. Each company and/or school gets to decide how their uniform looks and what is on them. There is no industry-wide regulation. If (and this is a big if) a Part 61 school has a uniform, it is usually a polo shirt and anything but jeans. Same with university programs. If you are in a Part 141 school, they decide what the stripes mean for their school. If you are working professionally in the industry then the stripes go as follows:
4 stripes equals captain regardless of type or level of experience.
3 stripes equals everyone else regardless of type or level of experience.
2 stripes equals the ever increasingly rare species called the flight engineer. They are nearly extinct.
1 stripe is not really used in the airline industry. It is sometimes used to signify a pilot trainee in some schools.
0 stripes means the company does not use stripes for your position.
Polo shirt equals cushy corporate job. Cayman Islands, here we come.
Remember, some people CHOOSE not to be captains. If you are a high seniority first officer, you go to the bottom of the captain seniority list as soon as you become a captain. That may be why they call it an upgrade instead of a promotion like they do in the military. Remember the name Jeffrey Skiles, a highly trained, skilled, and experienced pilot who contributed his teamwork to the Miracle on the Hudson.
Also
Graduating from a University with an aviation degree does not make you a pilot. There are many different NON-FLYING aviation degrees. The professional pilot tract of a university would get you a degree as well as the appropriate pilot certificates (PPL, Instrument, multi, comm-single, comm-multi, and possibly CFI/CFII/MEI). You would have to fly with an instructor as well as take university classes. The cost of the flight hours is usually in addition to your regular tuition.

Not to mention that many of us who are pilots don't wear any sort of uniform at all.  Most of my flying has been done in jeans and a t-shirt, with sweater or jacket as needed in colder weather.  If some aviation schools choose to require their students to wear uniforms with stripes, that's entirely their business.

Thanks for the merge. For future reference, here is the official guidance for multiple answers: What's our policy towards multiple answers from the same user on the same question?


text:
Why does TCAS need 2 antennas?
Can someone explain why TCAS needs 2 antennas (one on the top of the fuselage and one on the bottom)? And why is the top one directional and the bottom one can be either omnidirectional or directional?

Shielding effects of the fuselage

Two antennas
As @Ron mentioned the fuselage is an opaque obstacle for waves, and two antennas are required to cover the whole space around the aircraft. The choice is to have one antenna at the bottom of the fuselage and another one at the top. This is similar to SSR antennas, and actually SSR and TCAS, which share the same frequencies, can use the same antennas.

TCAS two-antenna system, source SKYBrary
When the bottom antenna sends interrogation pulses, these pulses can be reflected on the ground before reaching the intruder transponder, this very common effect is called multipath propagation, it can lead to false tracks, due to a wrong evaluation of the distance.
In addition it illuminates a large area below the aircraft down to the ground, this can trigger a lot of replies from other transponders, particularly from dense traffic at lower altitude, even if TCAS are inhibited at low very altitudes and on the ground, because TCAS also trigger mode C and S transponders. If a large number of replies reach the antenna at the same time, synchronous garbling is possible and some replies are not processed.
The solution is to use the top antenna as much as possible for long distance detection, and limit the bottom antenna to monitor intruders at shorter distance and below the aircraft. Other intruders are monitored by the top antenna. In practice, the lower antenna power is reduced.
Synchronous garbling reduction by whisper-shout
Different techniques are used to further limit garbling, as mentioned one is to reduce power when possible, and the protocol used by TCAS is to send pulses at low power more frequently than at hight power. This is known as the whisper-shout technique, and is also used for SSR.
Low power interrogations have a smaller effective radius and allow to get the short range picture, while the long range picture, which doesn't need to be refreshed as often, is obtained with high power interrogations.
However it is possible to further reduce synchronous garbling, specially at long range, by using directional interrogation pulses. While this technique is first used on the top antenna where is it most effective, it can also be used for the bottom antenna.
Synchronous garbling reduction by antenna directionality
The top antenna is made of at least 4 individual radiators which illuminate only 90°.

TCAS directional antenna, source
These individual antennas can be used together to form a radiation pattern in a given direction. This has two interests:

It reduces synchronous garbling on the antenna which is used most often. The effect is two-fold: In transmission, only aircraft in a 90° sector are interrogated; in reception replies from aircraft off sector are ignored.

It allows to determine the azimuth of a reply with some accuracy (1° to 10°). Sidelobes, also reduced by the antenna design, are used to refine azimuth processing.

See this document for more details.


text:
When starting a turbine helicopter, why should one slowly increase RPM (throttle)?
After the ignition switch is turned ON, my Captain always increases the RPM (throttle) very slowly.
I don't know why, because our helicopter has an ECU.
One day, my Captain asked me "Do you know why we increase RPM slowly?"
so I answered "umm, to prevent a hot start?"
Then my captain said "Nope. It is related to ENG OIL PRESSURE."
Is there any other reason about this slow operation (related to ENG oil pressure)?
Maybe compressor stall or surge?

Related: why-should-jet-engine-throttles-be-moved-smoothly?

Is there some reason why you decided to drop the subject with your captain and come here instead?

@Peter Kämpf  I read that article already. but i can;t found any relation about ENG oil pressure,,,

@Michael Hall because,,, captain set me a task,,,

Yes, you are right, there is no mention of oil pressure in the other answer. Pump pressure goes up with RPM and lubrication demands of bearings do as well. Since there is a delay in pressure buildup, spooling up slowly minimizes the oil pressure lag. That would be my answer.

he probably wanted to make sure the oil pump keeps up with the engine and bearings won't run hot, or that the oil circuit gets primed. turboshaft engines dont like it when running at idle, they tend to overheat; so it better be written somewhere that the engine rpm should be brought up slowly.
is important that whatever procedure, it comes out of the book. I would have expected your captain to direct you to startup procedure then mention the reason, so you could look it up rather than learn it by hearsay.

Well I hope he gave more of an answer than what you quoted above.
But it is indeed to do with oil - if you advance the throttle too fast, there is the potential for the engine's demand for oil to outstrip the oil pump/circuit's ability to provide it while things are still warming and spooling up. It's unlikely to immediately end in a catastrophic failure, but bearings and the engine itself will not be being lubricated and cooled appropriately for a period of time until the oil does catch up, which decreases service life of parts, and increases the possibility of something going wrong later.
This is really not much different to any other kind of engine, such as automotive - you don't really need to warm up a modern car, but you shouldn't thrash it in the first few minutes either, or again the demand for oil may exceed the oil system's ability to provide it.


text:
How can the cruise speed be larger than Vne?
I recently read the POH for a M20V, the advertising for this aircraft states that the top speed is 242 KIAS. The POH gives the Vne at 196/195 KCAL/KIAS.
I have found a similar discrepancy, the Vl3 (light sport aircraft) mentions the aircraft has a Vne of 165 KIAS, yet one of the engine choices gives the plane a max cruise speed of 195. I find these numbers confusing can anyone shed a light on this?

The reason is that cruise speeds are usually given in TAS (True AirSpeed) rather than IAS (Indicated AirSpeed) or CAS (Calibrated AirSpeed). See e.g. this answer for details on what these speeds are.
Have a look at the following plot showing TAS as a function of altitude for the two Vne speeds you gave (assuming ISA conditions):

You can see that the claimed cruise speeds are achievable above 14,000 ft for the M20 and above 11,000 ft for the VL3 without exceeding Vne.
You said that advertisement for the M20V claimed a top speed of 242 KIAS, but I think that is a mistake. It should be KTAS, not KIAS. Wikipedia also claims:

Cruise speed: 242 kn (278 mph, 448 km/h) (TAS)

(Wikipedia - Mooney M20)

So is VNE (at least on some A/C, maybe those where the VNE is dictated by flutter and not load factors), my A/C has a plaque reporting a decrease in IAS VNE with altitude.

@Caterpillaraoz You are right that Vne can depend on altitude, but it is always given in IAS or CAS, not TAS. For the Mooney M20, it just says Vne is 196/195 KCAS/KIAS in the  POH (see e.g. here). Even if Vne is lower at higher altitudes, the max. cruise speed will obviously be below that (after conversion from TAS to IAS/CAS) at that altitude.

The more i dig into this more more complicated the thing becomes.


text:
How can an aircraft door be modified to open in flight at cruising altitudes?
Just do a Google search for opening an airliner door in midair will spring up a dozen sites of why this is nearly impossible, if not possible.

And the difference between the inside of the plane and the outside can be huge. Which is exactly where the doors come in. Inside the cabin, 8 pounds of pressure push against every square inch of surface area. The typical passenger door is about 6 feet tall by 3 1/2 feet wide. So we're looking at more than 24,000 pounds of pressure bearing down on that exit.

Source: Why it's physically impossible to open an airplane door mid-flight
Another article from WP:
No, unruly passenger: You can’t physically open a plane door midflight
However, it seems the recently retired  NASA telescope carrying Boeing 747 (N747NA) could open a telescope POD while the plane is in midair:

Source: NASA bids farewell to SOFIA: the unique Boeing 747SP aircraft modified to carry a reflecting telescope made its last flight
So mean it's possible to open a door or hatch of an airliner in flight?

The door and aircraft would have to be specifically designed to do that. Typical aircraft and doors are not.

Can you clarify your question? It is not quite clear what you are asking about. Are you asking whether it is possible to open a normal airliner door, which is explicitly and specifically designed to be impossible to open during flight? Or are you asking whether it is possible to spend millions of dollars to modify an airliner and design and build a special door that is explicitly and specifically designed and built to be opened in flight?

Also, you posted a photo of an airliner with its door open in flight, so doesn't that photo already answer the question?

Here is a good description of how the SOFIA telescope is installed: "The telescope is located in the rear of the fuselage, which has a sealable opening. The passenger cabin and the telescope cavity are separated by a pressure bulkhead. During observations, the instruments and the scientists are in the passenger cabin and the telescope - when the hatch is open - is exposed to the conditions that exist outside the airplane."

Note on SOFIA: if you look the photos or the documentation, you see that the door is much larger then normal, but so it needs a lot of internal reinforcements: there is a lot of extra steel inside the aircraft to avoid deformations (both for pressurization and for the larger door). Some sky diving aircraft can do it (but usually they are not used on such high altitudes, which you didn't really specify).

The answer to your question, (like so many others) is : “It depends”.
Most airliner doors could be opened in flight, but ONLY if the aircraft is first depressurized.
Some other designs can be opened, even if pressurized, but usually only due to a mechanical failure.
There have been a few examples over the years of pressurized doors
opening inadvertently.
Here is one example:  Time Air F28 main cabin door opens in flight

Here is another F28 example: Airlines of Western Australia F28 main cabin door opens in flight

"usually only due to a mechanical failure" I take that to mean unlocked (disarmed) from the pilot's controls. But how does that account for the pressurisation differences of 20kpa bearing down on the door?

Pilots have no control over the operation of entry doors in the flight deck. Some designs can be accidentally opened, even when pressurized.  It depends on the design, and it depends on the failure.

@Nederealm i.e. some designs have to be opened inwards, which is impossible due to the 1-tonne-per-square-meter pressurization force pushing out. Some designs open outwards, and have mechanical locking mechanisms that stop them opening when pressurized, but sometimes the locking mechanisms break. (See the DC-10 cargo bay door!)


text:
Would plain and slotted flaps increase lift substantially in a distributed propulsion application?
Would plain and slotted flaps increase lift substantially in a distributed propulsion application for a slow moving aircraft (15mph)?
I understand that:

A classic NACA foil without flaps such as the NACA 650-18, as used on Zenith 701 STOL aircraft produces a maximum lift coefficient (Clmax) of approx. 1.5.

Add a plain non-slotted flap, and the Clmax increases to roughly 2.2.

Add slotted flaps, and the Clmax increases to roughly 2.8.

The maximum Clmax of distributed propulsion is 12.

Given a GA aircraft such as the Zenith 701, with an engine of 100HP, with a stall speed of 45mph, means the entire wing is bathed in air travelling at 45mph when flying at 45mph.

Assume the same given aircraft now has multiple propellers installed along it's entire leading edge in a distributed propulsion arrangement, with multiple engines totalling the same total Hp, flying at roughly 15mph and with an propeller exit speed of 45mph. This also means the entire wing is bathed in air travelling at 45mph. ( assume 100% efficiency, no swirl angle, etc.).

See graph below.
(Solid black graph - Source: Aviationchief.com. Added graphics estimated by the OP.)

As distributed propulsion is just "extra air", and flaps move the lift slope curve up and to the left, I would think the wing would see substantial increase in Clmax if plain flaps or slotted flaps added.

I understand that in distributed propulsion, a wing with a Clmax of 6, on a slow flying aircraft, (15mph), but prop exit speed 300% faster at 45mph, the local AoA would always be under 10 deg.

I would think there would be a substantial increase in lift when using a plain flap and even more when using a slotted flap, but almost no increase in Clmax above 10 deg AOA.

Is this correct thinking?

No, that thinking is incorrect.
The air involved in lift creation is roughly the amount that flows through a disk with a diameter equalling wing span, and your distributed propulsion concept will involve a far smaller amount of air.

The maximum Clmax of distributed propulsion is 12.

In theory maybe. Practical values are half that, at most. Now consider that this lift should ideally be independent of engine health and power settings, or you will plummet from the sky when power fails or you need to throttle back. Distributed propulsion will not save you from empty fuel tanks or batteries, so this scenario must be considered. Besides, the lift coefficients you cite in your question are valid for 2D flow; in reality the outer wing will contribute much less to provide some margin for control and stall behavior.

@ Peter Kamp: Good to know.  I think the Nasa's X57 boosts power from about 270 Hp to about 350Hp. What about adding plain or slotted flaps? Would there be a substantial increase in lift (as shown in the graph above) - a higher increase than without distributed propulsion, since flaps offset the lift slope curve up and to the left?

@Fred: In order to create more lift, you need to accelerate more air (higher span, higher speed) by a bigger amount (slats, flaps). Every bit helps. Adding props along the leading edge helps (but not by the amount you assumed) as does adding flaps. And slotted flaps work better than plain flaps. Double-slotted flaps with chord increase are even better. But also heavier, so more lift on the wing is needed for the same minimum speed. After adding enough gizmos you will run into diminishing returns.

Following your wing span example above, does that mean a wing with the same area, but half the span, and double the chord, needs 1/2 the air/mass flow to create the similar lift?

@Fred: No, it means it uses only a quarter of the air mass and will accelerate that by four times the amount that a wing of twice the span would need to accelerate the air mass it can influence. The area of the circle is proportional to span squared! This also means that induced drag is four times higher for the more narrow wing!


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Is designing a small GA airplane with a wing loading of 20-25 lbs/sq ft a bad idea, or is that wing loading too high?
Is designing a small GA plane like the following a bad idea?
This question is not the same asking if a an airplane with a traditional design is safer with a lower wing loading.
This question specifically asks if there are any reasons not to design a small slow landing plane such as a non-USA ultralight with a specific wing loading of 20-25 sq ft, and gives specific design suggestions to counter against popular reasons why an airplane shouldn't be designed at that wing loading.
Is designing a small GA plane like the following a bad idea?
Similar to the Cri Cri but with a wing loading of 20-25lbs/sq ft, slotted flaps, similar 17% airfoil to a Zenith 701, for low a weight spar, wing twist and vg's for better stall resistance,  twin engine, MTOW of 600 lbs, so wing area of 30 sq ft, 15 ft span, 2 ft chord, and a stall speed of 30-45mph (assuming all the math works out)?
This reduces the argument that high wing loading planes must land at a high speed and use low profile wings, which are easier to stall.
It seems many small airplanes are designed in the 10-14lbs/sq ft range, except for the BD5 at 17 lbs/sq ft (popular longer wings), and Rutan's Catbird at 45lbs/sq ft.
Wouldn't smaller wings, smaller spar, lower weight, less drag and less horsepower requirements be advantageous?
Approximate wing loading of various aircraft:
Cessna 172 - 14lbs/sq ft
CriCri - 11
Zenith 601 - 10
BD5 - 17
Rutan Catbird - 45lbs/sq ft

Where did you get the catbird figure? That doesn't seem right

I'm finding the Cirrus SR20 has a wing loading of 22.2 and the SR22 23.5, so it doesn't seem too out of line.

@ Fred Larson: Thanks for getting back to me. This is great news! Definitely going to design my plane in the 20-25lbs/sq ft range. Don't know why the moderators decided this wasn't important and decided to close this post -bad for aviation - good for me! If more designers designed planes in this range, aviation would look much different with longer distance flights, lighter planes and more places to land! Thank you!

Racing airplanes do that and live with high landing speeds.  25 psf is about the wing loading of a Beech Baron.  The Baron stalls in the landing configuration, gear and flaps down, at 84 mph/73kt.
This mean you fly approaches at 110 mph with flaps.  Not too many GA pilots are safe with an airplane that hot without a lot of extra training and lord help you if you have to put the thing in a field that fast (a single I mean, the Baron being a twin and the expectation of off field landings being low).
You can make the flaps fancier, and maybe get that down under 100 mph, and then add wing slats and maybe get it down to 90, but you just added a lot of weight and cost.  Not worth it for a few knots at the top.


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Which FARs does the Boeing 737 MAX conform to with respect to turbulence?
Based on this question/answer it seems that the FARs in relation to turbulence handling have been updated several times over the years. Does the Boeing 737 MAX conform to the latest FARs or to the FARs in place when the Boeing 737 was first certified?

Testing standards for things like turbulence and fatigue are not related to any specific aircraft type certificate. Yes, the MAX shares the same type certificate as the first 737-100, but the TC only makes reference to the certification standards to which the design complies. If you look at the TC you will see that it references the advisory circular for fatigue and damage tolerance testing (AC 25.171-1x), but as new models are introduced the TC makes reference to the latest version of the AC at the time the modified TC is issued to include the new model. The latest version of the AC is -1D.


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Is there a way to determine maximum rpm for axial compressor due to material limitations?
I'm looking for RPM to Stress relation to determine maximum rotational speed that compressor/turbine blades can have without undergoing deformation due to centrifugal tensile stress.
I've come come across this relation but I'm not sure if its correct one:
$$ v_t = \sqrt{\frac{\sigma}{\frac{1}{2} \times \rho \times \left[ 1 - \left( \frac{\Omega_h}{\Omega_t} \right)^2 \right]}} $$
where:

$\sigma$ is the stress (tensile) of the material
$\rho$ is the material density
$v_t$ is the rotational speed of Rota
$\Omega_h / \Omega_t$ is the Hub-Tip ratio


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Do biplanes need bigger tail volume coefficients than monoplanes?
Do biplane ultralights need bigger tail volume coefficients than monoplane ultralights?
Horizontal Tail Volume Coefficient
I understand that biplanes don't need a larger horizontal tail coefficients vs a monoplane of the same total wing area and same wing span. This is because the chord is would be half of the monoplane, but there are two wings, so the "total chord" is the same, so the horizontal tail volume coefficient does not need to increase. I'm told a typical tail volume coefficient for light airplanes is 35%.
I understand that the horizontal tail volume may actually be lower than that of a monoplane if the wings are staggered, the wings acting like a reflex wing and reducing the wing moment, so a smaller horizontal tail volume may be used in this specific case.
Vertical Tail Volume Coefficient
I understand that the vertical tail volume coefficient on a biplane is twice as large  as that of a monoplane with the same span, as there are two sections of span that the vertical tail needs to control. I'm told a typical vertical tail volume coefficient is 3.5% for light aircraft.
Is this correct?

Tail volume is a measure for the ability of the tail to compensate for the destabilizing pitch moment created by the wing in case of the horizontal tail and for adverse yaw in case of the vertical tail. This pitch moment is proportional to the square of the wing chord (one factor comes from the area, the second from the lever arm), so if you compare two otherwise equal designs, one of which is a biplane and the other a monoplane of twice the chord, the dimensionful horizontal tail volume (expressed as tail surface times tail lever arm) of that monoplane needs to be twice that of the biplane. To counter adverse yaw, however, the dimensionful vertical tail volume is the same.
Tail volume is normally made dimensionless by referencing it to the wing area and the mean aerodynamic chord (for the horizontal) or wing span (for the vertical tail). Since the area of both designs is the same and the MAC of the monoplane twice as large as that of the biplane, both dimensionless horizontal and vertical tail volumes become equal even though the dimensionful horizontal tail volume of the monoplane is twice as large.
However, if you compare wings of the same aspect ratio (which might be a better basis), both the chord and the wing span of the monoplane are larger by a factor of √2 but there is only one wing to consider versus two in case of the biplane. Now the dimensionful horizontal and vertical tail volumes for the monoplane are larger by a factor of √2.
Only when you make the chord of both wings equal (doubling the span of the monoplane in the process) will the dimensionful horizontal tail volume of both designs be equal but now the vertical tail volume needs to be twice as large.
Wing stagger with the same incidence on both wings would move the biplane closer to the monoplane with twice the chord whereas a lower incidence on the rear wing would indeed create that reflex effect and reduce the instability of the wing. Still, you need control power to change angle of attack quickly enough for maneuvering, so I would be careful with any further reduction of tail volume even if the staggered biplane wing by itself is stable already.

Do biplanes need bigger tail coeefficients than monoplanes (of equal wing area)?

Here's where building free flight models and testing them in cross wind conditions is very helpful.  As a designer, it is important to consider wing and tail functionality.  Many "tailless" designs, such as deltas, have adequate stability without a separate and distinctive "tail". Reducing chord and increasing aspect increases the need for a separate, stabilizing "tail".  Some designs put the "tail"(canard) in front to decrease stability and increase maneuverability.
You may find biplanes need a smaller vertical volume than a mono plane of similar wing area.  This is consistent with designs of 100 years ago, where "slab sides" also aided in lateral stability.
The testing for for vertical tail volume can be done by releasing the plane in a cross wind, and seeing if it "points" into the wind or turns away.  Many mono plane designs, particularly with excessive dihedral "effect", will roll and turn away from the wind.  Biplanes seem to be less prone to this, possibly due to a shielding effect of the lower wing to the upper wing from the cross wind.
Tests for adequate horizontal stabilizer size will include adequate directional and static stabilility, but also there is one very important aspect of inertial rotation effect for larger aircraft.  The horizontal stabilizer needs to be larger to arrest pitching momentum before it exceeds stall AOA and effectively reduce AOA faster than it increases from relative wind shift from downward acceleration as the plane "sinks" from loss of lift.  This issue is much less common in GA sized aircraft unless aft CG limit is abused.
One may also find a wider wing, or 2 "staggered" wings, reduces the need for a horizontal stabilizer.  But keep in mind using the wing as a stabilizer may reduce its efficiency of lifting, it's primary task.  Notice "flying wings" have yet to replace the classic "wing and tail" design of modern sailplanes, though they can be very stylish looking.
There are many factors which go into the sizing of the vertical and horizontal stabilizer. For a (low Mach number) recreational aircraft, adequate "anhedralling" (side area below the CG) helps eliminate the need for excessive V stab area, as well as a longer torque arm (longer fuselage).
Evaluation of 120 years of existing and proven aircraft design, and choosing the parameters of desired performance, may be more useful than "rule of thumb".  Essentially, it is a trade-off of stability, maneuverability, and drag before software is needed to keep one from crashing.

I believe the reason this answer has been flagged to be deleted is because it doesn't directly answer the question asked.  While this is good information, it doesn't answer the question: "Do biplanes need bigger tail volume coefficients than monoplanes?"


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Do twin engine airplanes have increased roll stability?
Do twin engine airplanes with counter rotating props have increased roll stability?
Imagine a gust of wind hitting the airplane from the front right quarter.
The gust hitting the front of the plane first would yaw the plane to the left, before the rear vertical stabilizer can counter the yaw, the airplane will then roll to the left as the right wing sees more lift.
With a twin engined aircraft, the left engine would counter that yaw.
If less yaw, would that mean less roll, and therefore more roll stability?
Is this correct thinking?
If not, what can be done to increase roll stability besides using a maximum dihedral of about 6 deg and the addition of ventral fins, and wing sweep?

It is not clear which direction you are imagining the wind gust coming from when you say "45 degrees to the right".  Also, in the non-counter-rotating case, couldn't possibly make a difference which side the wind gust was coming from?

Question or three. If the wind were coming from the right at 45° (in other words, a quartering headwind coming from the right), wouldn’t the aircraft weathervane (yaw) to the right? While airborne, would there be any tendency to roll since there would be a lack of ground friction? Wouldn’t the aircraft just have a different ground track and groundspeed versus heading and airspeed? In the absence of uncoordinated flight, would there be a lift differential to cause a rolling moment? If there was a rolling moment to the left, wouldn’t the yaw to the right balance it out? If not, please explain.

@Fred, could you explain what you mean by "would counter the yaw".  Are you thinking about gyroscopic effects, or moment ("weight") effects, or aerodynamic effects, or force effects ??  It's really unclear at the moment.

You're imagining the wind coming from the right, pushing the nose to the left. That doesn't happen. In fact, this is much more likely to push the nose to the right, because the vertical stabilizer, being a large panel that's far from the center of mass, creates a larger torque. This phenomenon is called "weathervaning", and is a huge concern for tailwheel planes and seaplanes particularly.
But, to get to the actual question: You are correct in thinking that, if a plane is yawing to the left, the outside wing is going to generate more lift, causing it to roll left. But, no, having multiple engines on an airplane will not stabilize it in either roll or yaw. For all the thrust from the left engine is doing to counter the yaw, the right engine's thrust is balancing it out, so a twin engine will not be any more stable than a single engine, all else being equal.

What about a larger moment of inertia conferred by weight displaced from the centerline of the craft? Is that at all significant, at least for large engines?

I see no basis for this answer TBH, more weight on the wings should increase roll inertia, which will have an effect on stability. Do you have any sources to back this up?

@Vroomfondel would seem to be perfectly correct, and in general, unfortunately this answer totally confuses me on a physics level.  It's not even clear which point it is addressing? (since the question is so confusing!)

@Vroomfondel I wasn't talking about gyroscopic effects at all. The OP mentioned that they thought the left engine, specifically, would compensate for yaw. I took that to mean that they were talking specifically about the torque from the thrust of the left engine, which is, in fact, compensated for by the thrust from the right engine. I'll add a bit to my answer to make that more clear.

@user2647513 Yes, having weight farther from the centerline would increase the moment of inertia, which would resist rolling slightly more. But the question (at least, as I understood it) was specifically about thrust, so that's what I addressed.

If one goes to an indoor arena with no wind and tosses gliders from the bleachers, 2 things will work:  dihedral and pendulum.
Dihedral provides roll stability by keeping the center of vertical lift in line with the CG.  This concept is easily seen in the relationship of wing and horizontal stabilizer/elevator (or stabilator) on the pitch axis.
Pendulum works the same way as in a parachute.  One may picture this mechanism as a parachute/glider that also moves horizontally.  It is lift (or drag) up, weight down.
Dihedral effect comes into play when you move outdoors and experience variable wind, or gusts, that are enough to perturb the aircraft so that it must "right" itself.
Now, we consider, the "dihedral effect" of wing sweep, wing dihedral, upright vertical stabilizer, fuselage side area above or below the CG, ventral fins, etc.  that effect roll once the plane is slipping and the relative wind is no longer directly from ahead.
This is where we generally throw away the "low pendulum", now aerodynamic forces around the CG are critical to good handling characteristics in a crosswind gust.  The wing dihedral is balanced with "anhedral effect" of side area below the CG, which can include big solid disc fixed gear, slab sided fuselage, and downward pointing vertical fin.
Adding perimeter weight towards the wingtips with 2 engines or fuel tanks will increase roll inertia, which is helpful for passenger comfort in a transient gust.  Higher wing loading also contributes.
But wing dihedral is a weak stabilizing force in a crosswind, and adding more will not work nearly as well as properly balancing side area above and below the CG.  The Cessna 172 is a living testament to this design.

Yes, twin engines will have increased roll stability compared to a single engine, all other things being equal.
As others have mentioned in comments, roll stability is directly impacted by moment of inertia. To be specific, it is determined by roll moment of inertia. For a derivation of the relationship see sections 4.3 (Representation of Aerodynamic Forces and Moments) and 4.3.1 (Longitudinal Stability Derivatives) of this publication. Moment of inertia is a product of mass and the square of its distance from the axis of rotation. Increase in mass or distance increases the moment and thus the stability.

Suppose we have two airplanes that are identical apart from the placement of the engines. Assume the mass, aerodynamics, and mass distribution (apart from engine) are identical. Let the engines of the first plane be very far from the longitudinal axis and the engines of the second plane very close to the longitudinal axis.
The equations indicate that the first plane will have a higher roll moment of inertia and higher roll stability than the second plane. Consider a force acting on the plane that causes some amount of roll. How much force would be required to rotate each plane by angle θ? While both planes would rotate by the same angle, the engines would move different distances, resulting in different amounts of work required. To move the first plane the same as the second, you need either an increase in force or time.

With respect to the relationship between yaw and roll, I can't speak to it but check out this paper on Longitudinal Static Stability. As best I can tell, it seems to me that there is a positive relationship between roll and yaw as described by "roll-yaw inertial coupling".

Any tendency for divergence in pitch is resisted by the much larger longitudinal static stability. This form of inertial coupling is known as ‘roll-yaw inertial coupling’.

this is very well presented, but you may want to dig a little deeper.  Roll inertia affects roll rate, but whether or not it wants to roll or not depends on the dihedral (which can help if wings so not perfectly match)(and, of course, the ailerons).  Dihedral stability is an interaction between center of vertical lift and CG.  Also, pitch stability is on a different axis than yaw or roll.

That's not the definition of roll stability. Roll inertia is just that...inertia. Stability is about restorative force (static stability).

$restorative force$, like it.


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Is the Bede BD5 actually a tandem wing airplane, and not a mono wing?
Is the Bede BD5 a tandem wing airplane, and not a mono wing?
The following picture (Source: Wikipedia.org) shows a Bede BD5 with a high angle of incidence on the horizontal tail, estimated at about 5 deg.
Being a rear engined airplane ( estimated fuel and engine north of 150 lbs) and with the main wing close to the pilot(150 lbs+), it seems the CG would be aft of the main wing.
Does this mean the vertical tail was used to generate some of the total lift (estimated at about 30%),in straight and level flight, thus making the BD5 a tandem wing, and not a mono plane?

No. The BD-5 uses a stabilator for the horizontal tail with a single wing. When parked and the gust locks are in place the stabilator is in the 'pitch down' position you see in the picture. As the whole surface moves, the apparent incidence is not present when in normal flight.

Why did Bede use a stabilator?  I assume it has something to do with the extremely short lever arm between the  tail and the cg?

I don't know why he did, but your assumption is a reasonable guess.


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Does the angular momentum of a jet engine affect aircraft performance?
I am interested, do jet engines have angular momentum? And how does such momentum affect airplane stability?

Possible duplicate of Do turbine engines on multi-engine aircraft rotate in opposite directions to offset torque?

Better to muse does any rapidly spinning object ever lack angular momentum?  Of course not.  The solution is to pair it with an identical oppositely rotating object or have some means of controlling its torque.  See helicopters and gyros to start.

This is not a duplicate of the other question. The OP is clearly referring to angular momentum (not torque differential) and its effect on aircraft stability, which was not addressed in the other question.

Angular momentum becomes torque differential when the orientation of the spinning object is changed, much like a spinning bicycle wheel in your hand.  Some studies were done on the effect of the rotating (single) jet engine on the spin characteristics of an F-104, basicly making a complete mess of it due to gyroscopic effects.  Don't have enough hard info to post, but OP is on the right track.


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How is a misdeclared weight of a mail bag handled?
What is the proper process when a postal administration tenders a mail bag with under declared weight?
Is the bag returned to the postal administration or is the bag weight altered to match the actual weight or is there no weight verification of mail bags?

Are you thinking about mail that is transported in the cargo hold of passenger airplanes? That cargo is usually transported in ULDs, which are weighed as a whole before loading.

Could you clarify what is the aviation-related aspect you're asking about?

You may precise if your question is more about weight and CG computation or more about cargo handling and facturation or about something else. I think you may begin by a question about weight verification mechanism only to avoid too broad questions.


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Can you identify this model of a twin-engine propeller aircraft?
Can anyone tell me what this is please?

It resembles I.AE. 24 and I.AE. 30, but not close enough for a match.
I believe this is a model of the De Havilland Mosquito.

Image source: ThoughtCo.

It's not a true scale model of any real aircraft; it looks like a cross between a Mosquito and a Westland Whirlwind.

yeah, it's a toy taking inspiration from several real aircraft, and those two are the most obvious ones

I believe this is a De Havilland Hornet, though as user44163 says it's hardly a good model.
Clues for me include the colour (suggests a high-altitude aircraft) and the relatively small canopy.  But the model is not representative, so it's impossible to ID properly IMO.
https://en.wikipedia.org/wiki/De_Havilland_Hornet


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What is the standard date format used in aviation?
As English is the standard language used in aviation and Zulu/UTC time is used as standard too or at least between pilots to calculate flight time and fuel. Is there any standard date format used in the industry like ISO 8601 (YYYY-MM-DD)?
https://en.wikipedia.org/wiki/ISO_8601

I'm not sure if there is really an industry wide standard for the date format, but at least the ICAO (International Civil Aviation Organization) uses the YYMMDD date format for flight plans:

DOF/ The date of flight departure in a six figure format (YYMMDD, where YY equals the year, MM equals the month and DD equals the day).

(FAA on ICAO flight plans)
Other flight plans may use different formats however. See e.g. the following example of a LIDO flight plan (Lufthansa Systems format):

(image source: SimBrief.com)

Depends a bit on where the date is used.
For flightplans, the Date Of Flight (DOF) should be inserted in item 18 in the format YYMMDD (for example 200816 for the 16th of August 2020).
In a NOTAM, a format similar to the DOF flightplan format is used, but usually with the addition of four digits to indicate the time (HHMM):
C0424/20 NOTAMN Q) EKDK/QWGLW/IV/M /AW/000/060/5601N00901E005 A) EKAB B) 2008061000 C) 2008162000 D) DAILY 1000-2000 E) INTENSIVE GLIDER FLYING WILL TAKE PLACE AROUND ARNBORG AIRFIELD EKAB PSN 560043N0090045E. F) SFC G) 6000FT AMSL
As for aeronautical publications:

4.2.3        Each  AIP  shall  be  dated.  In  the  case  of  AIP  issued  in  loose-leaf  form,  each  page  shall  be  dated.  The  date,  consisting of the day, month (by name) and year, shall be the publication date or the effective date of the information.

ICAO Annex 15
This typically means 16 AUG 20, 16 AUG 2020 or 16 AUGUST 2020.


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Why don't we see diverging nozzles or diffusers?
When it comes to fully subsonic propulsion, all outlets are converging nozzles (I did say fully subsonic so no converging diverging). From what I understand, they are flow regulating devices (changing the exit diameter allows to control the mass flow through the propulsion system, be it a turbofan or ducted electric fan).
Why don't we ever use diverging outlets, i.e. diffusers? Is it due to the back pressure? Wouldn't such a shape increase the pressure recovery, i.e. more thrust.

"Wouldn't such a shape increase the pressure recovery" - The pressure recovery is the pressure immediately forward of the fan, divided by the free stream total pressure, isn't it? How would a diverging outlet increase the pressure immediately forward of the fan? Maybe I'm totally misunderstanding something.

sorry, i meant the after the fan. by turning the speed into pressure

The basic answer is that pressure differential at the exit isn't what you want for thrust.  You want the exhaust stream to have velocity.  If it exits the nozzle with excess pressure, that extra pressure essentially gets converted into plume size (see the underexpanded streams on rocket first stages at high altitudes as an example).
This is why subsonic nozzles converge, and supersonic nozzles converge to a Mach 1 throat and then diverge.

"If it exits the nozzle with excess pressure, that extra pressure essentially gets converted into plume size" yeah but that pressure creates forward thrust on the diffuser walls, unlike a nozzle which is a dragful components. wouldnt that increase the overall thrust, despite the plume size?

I think that maybe the disconnect is that yes, having higher-pressure gas on the exit side of the engine than the inlet DOES generate some thrust.  But The Environment around the aircraft is big, and a lot of that pressure/potential energy goes into just pushing around air in the environment.  It's more efficient to convert the pressure into momentum, which is a nozzle's job.  You can only trade momentum for other momentum, but you can trade the potential energy of high-pressure gas for heat and noise and other not-thrusty things.


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Literature request for effect of Aspect Ratio and Wing Sweep on critical angle of attack?
So I'm trying to find academic literature detailing how both aspect ratio and taper ratio affect the critical angle attack of an aerofoil - namely for a v. low AR wing (AR<1), and high sweep (~75 degrees), i.e. where vortex lift dominates at high AoA.
The best I've found so far this the diagram below from Roskam detailing changes in Clmax with flaps for different planform dimensions, but no joy, including reviewing Raymer, and Nikolai's fundamental aircraft design books.
Anyone know any good literature outlining stall angle by varying these two parameters?

I'm pretty sure results like that have been published as a NACA or NASA technical report at some time, which I hope is academic enough for you, but I don't know one off the top of my head.